1. Field of the Invention
The present invention relates to an antimicrobial caries detecting composition for use in the odontological treatment of caries-infected teeth, which composition selectively stains the portion of a tooth which is infected with carcinogenic microbes, prior to removal of the infected dentin of the tooth, thereby facilitating the removal of the infected portion of the tooth. More particularly, the present invention relates to a composition which is capable of sterilizing and staining the infected portions of teeth at the same time.
2. Description of the Background
In the conventional treatment of tooth caries which removes the dentin infected with cariogenic microbes, the infected portion is selectively stained so as to clearly differentiate the infection from the non-infected portions, thereby removing the infected dentin as completely as possible. In order to achieve this objective, Japanese Patent Application (JPA) Kokai No. Sho-51-38428 discloses a "caries-detecting composition" which comprises a basic fuchsine and a mono- or polyalcohol, and shows some effectiveness. However, even with the development of such a cartes-detecting composition and its wide-spread commercial use, there is still no end to the reports of pulp irritation after caries treatment, which is a serious problem in the field of dentistry.
On the other hand, in order to prevent caries, JPA Kokai No. Sho-51-38427 discloses as its objective, a "dental plaque or calculus-detecting composition", which is used to stain the dental plaque or the like which adheres to the tooth surface thereby causing caries. JPA Kokai No. Sho-56-96700 discloses a "caries activity-indicating composition", which is used with sufficient daily teeth brushing and thereby provides an evaluation of the degree of danger of dental plaque. The former composition comprises a dye which is dissolved in a polyalcohol and/or water, while the latter composition comprises a pH indicator which is dissolved in an aqueous solution of a water-soluble polymer to which is added an antibiotic or preservative selected from chloraphenicol compounds and sodium azide compounds.
The cause of the dental pulp irritation, which has been discussed in those proposals, most probably is attributable to the penetration of the restorative component into the dental pulp. Various studies have been made on this penetration. However, it has been found that even if the restorative component itself is embedded adjacent to dental pulp, no serious irritation results. In this regard it has been recently proposed, as a component of the theory of bacterial cariogenesis, that the secondary invasion of oral bacteria into a cavity and the failure to remove the carcinogenic microbe-infected portion of a tooth, causes dental pulp irritation. In fact, recent studies into the prevention of secondary invasions of oral bacteria into cavities have been directed to increasing the adhesiveness between the dental pulp and the restorative material applied thereto in order to improve the sealing the margin of the restorative material. As a result, recent advances have achieved a very high level of adhesion between the dentin and the restorative material. Accordingly, cases of dental pulp irritation have decreased in recent days. However, it can not be said that there have been no reports of dental pulp irritation after caries treatment.
The cause of dental pulp irritation which appears to remain is the failure to remove all of the caries-infected dentin and the contamination of cleaned cavity with caries-infected tissue pieces that have just been removed from the cavity before the application of a restorative material thereto.
In the work leading to the present invention, the present inventors have assiduously studied various materials which would enable the complete removal of the carcinogenic microbes-infected portions from teeth and/or elimination of the contamination by the once-removed infected dentin from the cleaned cavity. The following has been found.
(1) A caries-detecting composition can not completely penetrate into the deepest portion of the caries-infected portion of teeth by one application, if the infected portion is thick. Therefore, a dentist repeatedly applies the caries-detecting composition to the affected area of a tooth to confirm the infected part, and then bores a cavity in the affected part. However, if the dentist has failed to finally stain the infected portion in the last test for infected matter, it is probable that carcinogenic microbes have not been completely removed.
(2) At the point at which the removal of the infected dentin is almost finished, it is often difficult to determine whether or not the dentin had been stained, so that removal of the infected dentin is often incomplete. In the case the cavity bottom is too thin, the cutting tool used would often penetrate the dental pulp. In order to prevent this problem, the operating dentist would often stop the removal of the seemingly slightly stained part.
(3) A so-called smear layer comprising powdered dentin is inevitably formed on the surface of the dentin from which the infected portion has been removed. It is likely that bacteria will remain in the smear layer.
(4) Since dentinal tubules are found in the surface of the dentin which has been drilled for the removal of the infected portion of the tooth, the smear layer is pressed into the dentinal tubules thereby forming a plug. It is said that the smear plug remaining in the opening of the dentinal tubules has an important role in protecting dental pulp from the components of restorative materials. It is likely, however, that the plug may be infected with carcinogenic microbes.
(5) Another possible source of contamination is the highly-contaminated dentin pieces which are scattered around the infected tooth during removal of the infected portion. This material is mixed with body fluids such as saliva, and likely again contaminates the affected portion. No attempts have been made to solve the possible problem of item (5).
The failure to remove any infected dentin must be solved. However, even if the infected dentin can not be completely removed or even if the infected dentin contaminates the affected portion, such should not cause cariogenesis if the bacteria existing in the infected dentin are inactivated. In order to achieve inactivation, if the cavity formed in an infected tooth is treated with a microbiocidal solution which is effective against cariogenic microbes, the object of the invention can be attained. Some trial reports have been introduced at various meetings of dental societies and in various odontological journals. However, even if carious cavities are treated with a microbicidal solution, the question of whether or not the microbiocidal solution penetrates throughout the entire region of the infected dentin depends on the thickness of the infected dentin. The pulp cavity has its own inner pressure, and the inner fluid in dentinal tubules flows from the pulp to the surface of the tooth. Therefore, even if a microbiocide is applied to the surface of the infected dentin, it is in fact difficult for the microbiocide to effectively penetrate into the inner depth of the infected dentin. Accordingly, if the infected dentin is thick, it is likely that the microbiocide applied thereto is often ineffective. After having made repeated studies to solve the above-mentioned problems, the present inventors have reached the following conclusions:
(1) When a caries-detecting composition is used to stain infected dentin while simultaneously sterilizing the dentin, the powdered dentin formed during a subsequent step of removing the dentin is sterilized. Therefore, the danger of dental pulp irritation, because of contamination of the powdered dentin in the affected portion, is greatly reduced, and even the danger of contamination of the adjacent teeth and the gums is reduced. Further, the possibility of infection from the tools that may induce additional cariogenesis is also greatly reduced.
(2) Where the infected dentin is removed and is simultaneously stained for caries detection and sterilization, the infected dentin is well-sterilized while its thickness is reduced. Here, even the bacteria existing in the depths of the affected portions can be effectively killed. In particular, after the last staining for the final confirmation, no infected dentin exists in the cavity. Even if some bacteria have readhered to the affected portions, they shall be completely free of bacteria. Under these conditions, therefore, satisfactory treatment is ensured. On the basis of these findings, the present inventors have made the following studies in order to find an antimicrobial caries-detecting composition.
The microbiocide which is employed in the present invention may be any and every known type that has been used in detergents and microbicidal compositions for dental use. However, (1) preferred microbiocides are those which are capable of killing 99% or more of 10 thousands of bacteria per 1 cm.sup.3 with a solution having a microbicidal concentration of 1000 .mu.g/ml for 10 seconds, wherein said bacteria include Mutans streptococci I and Lactobaclli, which are said to be cariogenic bacteria, Streptococcus mitis, and Actinomyces viscosus, which are said to be bacteria that may have cariogenicity, and strictly anaerobic bacterias which are said to cause dental pulp irritation.
(2) The microbiocides must be soluble in water and/or water-miscible solvents.
(3) When stored in the composition of the invention, the microbicides must be stable for a long period of time, and must not discolor the dye which is essential to the composition.
Among conventional microbiocides, preferred are cationic microbiocides, biguanide-type microbiocides, halogenated diphenyl ethers and analogues thereof, as suitable microbiocides for the present invention. Of these compounds, more preferred is at least one compound selected from the group consisting of cetylpyridinium hydrochloride, chlorhexidine, trichlosan and irgasan, or a mixture of two or more of these compounds.
More preferably, the caries-detecting composition of the invention still has some additional activity even in the stage of treatment after the removal of the caries-affected portion. Specifically, a polymerizable antimicrobial compound having both an antimicrobial group and a polymerizable group in the molecule does not interfere with the subsequent application of a dental adhesive to the surface of the tooth, even though it remains on the surface of the dentin, and, in addition, the antimicrobial compound copolymerizes with the adhesive to reinforce the adhesive layer during the restorative operation. Being different from other antimicrobial compounds that do not polymerize but remain as they are, the present polymerizable antimicrobial compound remains in the restorative material while being chemically bonded to the material after the dental treatment. Considering adhesion durability, therefore, the polymerizable antimicrobial compound is expected to exhibit remarkably safe effects. In addition, a compound of this type is further expected to modify the surface of the dentin so that it is more compatible with dental adhesives. The present inventors have found that, as an antimicrobial compound of this type, preferred are one or more polymerizable antimicrobial compounds having a (meth)acryloyl or styryl group and a quaternary ammonium salt group in the molecule, which are represented by formula 1 through formula 4.